Seismic prospecting operations in wells or wellbores imply the setting of an array of sensors such as geophones and the acoustic coupling thereof with the formations surrounding the well. The sensors are preferably arranged at various successive depths and linked to a surface installation through cables. The acoustic or seismic signals received by the sensors in response to the emission of seismic waves in the ground, following reflections on the subsoil discontinuities, are transmitted through the cables to a surface recording station. French patent applications FR-2,593,292 (U.S. Pat. No. 4,775,009) and 2,642,849 (U.S. Pat. No. 4,986,350) mention a well-known technique for setting stationary sensors in a well fitted with a casing held up by cementing. The sensors are fixed to the outside of the casing before it is lowered into the well, the linking cables running along the outer wall thereof, and the whole of the reception device with the cables is embedded in the cement that is then injected into the annular space between the well and the casing. An electronic preamplifying and filtering module may be associated with the sensors of a single level. The sensors and the modules thereof may be included in protection boxes arranged along casing sections or included in fittings between the successive casing sections, as described in patent application FR 91/11,536.
A well-known solution for connecting electrically together several boxes such as those mentioned above consists of using sealed electric connecting elements. These connecting elements generally comprise a connecting sleeve fitted with mechanical fastening means for a linking cable, a single- or multi-pin electric connector to connect all the lines of the cable, comprising sealed crossings for the various lines, and mechanical connecting means fitted with seal gaskets for fastening the sleeves to each box. An example of a connecting element, both mechanical and electric, between a well sonde and a multicore cable, is described for example in patent FR-2,615,044 (U.S. Pat. No. 4,874,328). Because of the relative complexity thereof, these elements can hardly be used to interconnect a large number of reception units such as those mentioned above. Difficulties and operating costs grow rapidly as the number of units increases because the number of sealed interfaces has to be increased at the level of the interconnections between them and the cable elements, in order to keep the inner space of each reception unit closed and electrically insulated.